The present invention is concerned with coupling of electromagnetic waves between rectangular waveguides and circular waveguides through the magnetic fields of such waves.
Coupling of such electromagnetic waves, between the TE.sub.10 mode in the rectangular waveguide and the TE.sub.01 mode in a circular waveguide has generally been accomplished in the past by arranging the waveguides in contact with each other with the longitudinal axes of both waveguides aligned in parallel. With such a coupling arrangement, the dimensions of the rectangular and circular waveguides must be selected so that the two modes to be coupled have the same phase velocity. The two waveguides are then provided with a plurality of coupling apertures along their common contacting wall. This type of coupling arrangement is illustrated in the U.S. patents to Unger, U.S. Pat. No. 3,184,695, and Miller, U.S. Pat. No. 3,529,205.
When the phase velocities of the waves supported within the two waveguides have been different, couplers have been built in which the longitudinal axes of the two waveguides have remained in a parallel relationship but a periodic phasing or periodic spacing has been provided in the coupling apertures. This approach has been discussed in a paper presented by S. E. Miller in Bell Systems Technical Journal, Volume 47, Oct. 1968, pages 1801-1822, entitled "On Solutions for Two Waves With Periodic Coupling".
An alternative approach which has been utilized for making transitions of electromagnetic waves between rectangular and circular waveguides is illustrated in the patents to Walker, U.S. Pat. No. 2,766,432 and Marcatili, U.S. Pat. No. 2,963,663. In the coupling arrangement illustrated by the patent to Walker, for example, the electromagnetic waves of the two waveguides are coupled through their transverse fields. The rectangular waveguide is wrapped around the circular waveguide with a plurality of coupling apertures being provided along the common wall, with the apertures being spaced by one wavelength. Since it is the transverse fields which are being coupled, the rectangular waveguide must be arranged with its wider wall in contact with the circular waveguide since this is the location of its transverse field component. When forming the waveguide coupler in such a manner, if it becomes desirable to provide additional coupling apertures than would be permitted by one turn of the rectangular waveguide around the circular waveguide, it is possible for the rectangular waveguide to be wrapped in a spiral direction around the circular waveguide, as pointed out in the patent to Walker (in column 3, lines 22 through 45).
While it would be desirable to provide a coupler arrangement for coupling the electromagnetic waves via their magnetic fields in an efficient manner without high degrees of loss and additionally to provide a coupler which would not consume a great deal of space, none of the previously utilized arrangements enable such results to be achieved. Where the couplers are arranged with their longitudinal axis in parallel, large lengths of couplers are required, on the order of 1.5 meters, such couplers generally tend to be narrow band and to have a low power transfer efficiency.